Band Gap Tunable, Donor−Acceptor−Donor Charge-Transfer Heteroquinoid-Based Chromophores: Near Infrared Photoluminescence and Electroluminescence

A series of D-π-A-π-D type of near-infrared (NIR) fluorescent compounds based on benzobis(thiadiazole) and its selenium analogues were synthesized and fully characterized by 1H and 13C NMR, high-resolution mass spectrometry, and elemental analysis. The absorption, fluorescence, and electrochemical properties were also studied. Photoluminescence of these chromophores ranges from 900 to 1600 nm and their band gaps are between 1.19 and 0.56 eV. Replacing the sulfur by selenium can lead to a red shift for emission and reduce the band gaps further. Interestingly, compound 1 exhibits aggregation-induced emission enhancement effect in the solid state. All-organic light-emitting diodes based on M1 and M2 were made and exclusive NIR emissions above 1 μm with external quantum efficiency of 0.05% and maximum radiance of 60 mW Sr−1 m−2 were observed. The longest electroluminescence wavelength reaches 1115 nm.